The present invention relates to an enzyme curable alkyd composition, particularly an alkyd composition cured with a radical producing oxidoreductase.
The quality and degree of ambient film formation in coatings is critical to performance. Film formation is typically achieved by evaporation, coalescence, or crosslinking, and combinations thereof. Evaporation-based film formation (also known as lacquer) is based on low solids content and large amounts of organic solvents. Though evaporation is one of the fastest and simplest methods of achieving film formation, it is severely limited by environmental legislation that limits the release of large quantities of solvent into the atmosphere. As a green alternative, film formation by coalescence has become more main stream. Nevertheless, coalescent methods, especially for high Tg polymers, can require the inclusion of a small amount of a volatile solvent to plasticize the polymer, thereby promoting film formation. Low Tg polymers (soft polymers), while not requiring solvent to promote film formation, produce films with inherently poorer performance.
To counteract the problems associated with softness, manufacturers of high-performance coatings rely on reactive polymer precursors to build up three-dimensionally cross-linked networks. Materials and compounds used to produce ambient temperature cross-linked polymers include drying oils, benzophenone, diacetone acrylamide/adipic dihydrazide, carbodiimide, ambient epoxy/acids, isocyanates, aminoplasts, and silanes. Although these precursors provide performance benefits, such as improvements in hardness, mar, print, dirt pickup, and chemical resistance, each has associated pitfalls such as pre-cross-linking, reliance on 2-component architecture, and potential toxicity as with metal driers like cobalt naphthenate.
In another approach, WO2004/067582 describes a method of introducing functional groups into a polymer to promote enzymatic oxidative curing. The method also requires a multi-component system and a thiol-functional compound, e.g., pentaerythritol tetrakis(3-mercaptoproprionate). However, introduction of thiol functionality into coating compositions is known to have adverse effects on pot-life (thiols are known to initiate premature cross-linking), as well as odor.
It would therefore be an advance in the art of ambient temperature cured coatings to find a curable film forming composition that has long shelf stability and a reasonably fast cure time, and does not require VOCs or malodorous chemicals.